Groups of 12 weanling Osborne-Mendel rats were fed diets containing 0, 0.1, 1, 5 or 56 percent sucrose. Each rat was caged singly with a donor rat that was infected with Streptococcus mutans 6715-15. The recipient and donor were swabbed daily and the bacteria were cultured on Mitis Salivarius agsr. Recipient rats fed 56 or 5 percent sucrose became infected with high levels of S. mutans. Recipients receiving low sucrose diets remained free of infection for much longer and when infected harbored lower numbers of organisms. The donor rats fed no sucrose failed to retain infection with S. mutans. Antibody analyses await completion.